1. Field of the Invention
This invention relates generally to a semiconductor technique and more particularly to a silicone polymer insulation film on a semiconductor substrate and a method for forming the film by using a plasma CVD (chemical vapor deposition) apparatus.
2. Description of Related Art
Because of the recent rise in requirements for the large-scale integration of semiconductor devices, a multi-layered wiring technique attracts a great deal of attention. In these multi-layered structures, however, capacitance among individual wires hinders high speed operations. In order to reduce the capacitance it is necessary to reduce the relative dielectric constant of the insulation film. Thus, various materials having a relatively low relative dielectric constant have been developed for insulation films.
Conventional silicon oxide films SiOX are produced by a method in which oxygen O2 or nitrous oxide N2O is added as an oxidizing agent to a silicon material gas such as SiH4 or Si(OC2H5)4 and then processed by heat or plasma energy. Its relative dielectric constant is about 4.0.
Alternatively, a fluorinated amorphous carbon film has been produced from CxFyHz as a material gas by a plasma CVD method. Its relative dielectric constant ∈ is as low as 2.0-2.4.
Another method to reduce the relative dielectric constant of an insulation film has been made by using the good stability of Sixe2x80x94O bond. A silicon-containing organic film is produced from a material gas under low pressure (1 Torr) by the plasma CVD method. The material gas is vaporized P-TMOS (phenyl trimethoxysilane, formula 1), which is a compound of silicon bonded to a phenyl group. The relative dielectric constant ∈ of this film is as low as 3.1. 
A futer method uses a porous structure made in the film. An insulation film is produced from an inorganic SOG (spin-on glass) material by a spin-coat method. The relative dielectric constant ∈ of the film is as low as 2.3.
However, the above noted approaches have various disadvantages as described below.
First, the fluorinated amorphous carbon film has lower thermal stability (370xc2x0 C.), poor adhesion with silicon-containing materials and also lower mechanical strength. The lower thermal stability leads to damage under high temperatures such as over 400xc2x0 C. Poor adhesion may cause the film to peel off easily. Further, the lower mechanical strength can jeopardize wiring materials.
Oligomers that are polymerized using P-TMOS molecules do not form a linear structure in the vapor phase, such as a siloxane structure, because the P-TMOS molecule has three Oxe2x80x94CH3 bonds. The oligomers having no linear structure cannot form a porous structure on a Si substrate, i.e., the density of the deposited film cannot be reduced. As a result, the relative dielectric constant of the film cannot be reduced to a desired degree.
Further, the SOG insulation film of the spin-coat method has a problem in which a cure system after the coating process is costly.
It is, therefore, a principal object of this invention to provide an improved insulation film and a method for forming it.
It is another object of this invention to provide an insulation film that has a low relative dielectric constant, high thermal stability, high humidity-resistance and high oxygen plasma resistance, and a method for forming it.
It is a further object of this invention to provide a material for forming an insulation film that has a low relative dielectric constant, high thermal stability, high humidity-resistance and high O2 plasma resistance.
It is a still further object of this invention to provide a method for easily forming an insulation film that has a low relative dielectric constant without requiring an expensive device.
One aspect of this invention involves a method for forming an insulation film on a semiconductor substrate by using a plasma CVD apparatus including a reaction chamber, which method comprises a step of introducing a material gas of a silicon-containing hydrocarbon compound expressed by the general formula Sixcex1Oxcex2CxHy (xcex1, xcex2, x, and y are integers) to the reaction chamber of the plasma CVD apparatus, and a step of forming an insulation film on a semiconductor substrate by a plasma polymerization reaction wherein mixed gases made from the gaseous silicon-containing hydrocarbon compound is used as a reaction gas. It is a remarkable feature that the residence time of the material gas in the reaction chamber is lengthened. According to the present invention, a silicone polymer film having a micropore porous structure with low relative dielectric constant can be produced. In the above, plasma CVD includes CVD excited by microwave.
The present invention is also drawn to an insulation film formed on a semiconductor substrate, and a material for forming the insulation film, residing in the features described above.